In mobile phones the operational input provided by the user in order to control the operation of the mobile phone is generally provided by keys in a keypad. For example a telephone number is usually dialed by pressing dialing keys. However, there are situations when it would be reasonable for example to select a telephone number or to provide some other control commands by using a system where it is not necessary to use the keys in the keypad.
U.S. Pat. No. 6,314,166B1 presents a method for dialing a telephone number by voice commands, i.e. without pressing keys in a keypad. Thus the user can select a telephone number by simply speaking it to the microphone of the mobile phone. The electric signal generated by the microphone is amplified in a microphone amplifier, filtered in a filter and digitized by a Analog to Digital-Converter (ADC) or alternatively digitized by a audio Coding and Decoding unit (CODEC) and thereafter voice recognition is performed on the resulting digital audio signal by a recognizer unit, typically a Digital Signal Processor (DSP), in order to parse the various commands, names, letters and numbers used in Voice Dialing.
The recognizer unit has a control unit, a processor, a speech pattern memory and a program memory containing the needed control and recognition algorithms. The recognition can also be performed for the user by a network element in the cellular system. In this case only the initiating of voice control needs to be performed by the mobile phone.
The mobile phone can also be used as a conventional mobile phone, wherein the dialing of the telephone number can be performed by using the keypad in the usual manner. In the voice controlled mode audio signals are received via the microphone, amplified in the microphone, amplifier, filtered and digitized and conducted in digital form to the recognizer unit. On the basis of the audio signal received, the recognizer unit calculates the corresponding one or several feature vectors which are processed by the recognizer unit in order to find out which command or number was uttered by the user. This kind of “key-free” operation mode is very useful for example in automobiles as so-called hands-free modes, wherein the driver of the vehicle does not need to loose hold of the steering wheel for dialing a telephone number.
However, voice recognition is relatively complicated and prone to recognition errors in a noisy environment, for example where the voices of other persons can be heard. Therefore the voice recognition for voice dialing is normally only activated when needed, otherwise normal ongoing conversations might trigger embarrassing or costly calls. Thus the initiating of voice control mode like voice dialing is seldom done by voice commands. The preferred method has been to use a special button to initiate voice control mode. However, in modern cellular phones the trend is to have as few buttons as possible. Thus the same button is used as a soft key for many purposes depending on the functional mode. Finding the right key combinations without looking at the keys or the display is not easy and by itself negates the convenience of voice dialing in prior art mobile phones.